Basic lead salicylates and process for preparing same



Patented June 3, 1947 BASIC LEAD SALICYLATES ANDPROCESS FOR PREPARINGSAME Leonard M. Kebrich, Brooklyn,

N. Y assignor to National Lead Company, New York, N Y., a corporation ofNew Jersey No Drawing. ApplicationMarch 15, 1946, Serial No. 654,801

Claims.

This invention relates to basic lead salicylate compositions and to amethod for preparing the same.

The present application is a continuation-inpart of co-pendingapplication, Serial No. 462,769,

filed October 1942.

The only lead salt of salicylic acid whose existence is generallyaccepted in the chemical literature is normal lead salicylatecorresponding to the formula Pb(CeH40'I-ICOO) 2, which may bemonohydrated by the addition of 1 mol H2O. This? salt, according to theprior art, was C0111- Inonly preparedby mixing solutions of a solublelead salt such aslead acetate or lead nitrat and it 462,769, filedOctober 20, 1942, it was observed that two basic lead salicylates, thepentabasic and monobasie, were formed before the normal salt was finallyobtained. These are formed successively upon the introduction of moreand more salicylic acid to a given slurry of lead oxide. The process ofthe present invention differs from prior methods in that the manner ofreacting the salicylic acid with a slurryof lead oxide. is carried on soas to produce an orderly succession of chemical reactions, controlled byobserving the pH of the solution. Furthermore, the economical advantagesof this invention over the prior art method of precipitating fromsolutions is readily apparent to those skilled in the art, in that theuse of large volumes of Wash water is avoided and the yield of theproduct is substantially complete. Thus the products of this invention.are obtained with a minimum of handling and no Washing, in a state ofhigh'puritywithout further treatment, except the usual flushing orfiltering.

and drying. If a filtrate is obtained, it may be recycled and usedagain.

According to this invention, a, slurry of lead.

oxide, (litharge, PhD) in water is prepared. Agitation is provided andto this suspensionis added, at a slow, uniform rate, salicylic acideither dry or as a water slurry to form first the pentabasic and laterthe monobasic salt, all "as more fully described below. The reactiontakes place between the lead oxide and the salicylic acid atroomtemperature Without the. presence of a water-soluble lead salt, such asthe acetate, nitrate, and the like, which accelerate the reaction.However, such accelerators may be used-insmall amounts, particularly ifit is desired to prepare the pentabasic salt which corresponds to theformula 5PbO-.Pb(CsH4OHCOO)2. This salt is an entirely new composition:of matter.

When more salicylic acid is added tothe' sus-- pension of pentabasiclead silicylate, the pH value remains constant until the solid phasecontains one mol of salicylic acid per mol: of. lead oxide at which timethe solid phase consists of monobasic lead salieylate, whichcorresponds-to the formula PbO.Pb(Csl-I4OHC0O) 2. This also is anentirely new composition of matter.

On the addition of' salicylic acid to the lead oxide slurry, the pHremains constant at about 9.9 until pentabasic lead salicylate is formedat which time there is an abrupt change in pH from about 9.9 to about8.3. On the further. addition of salicylic acid, the pH remains constantat about 8.3 until all the pentabasic salt is combinedwith salicylicacid to form the monobasic salt. The

completion of the. formation of the monobasic salt is accompanied by an.abrupt change in. pH.

from about. 8.3 to about 4.8. According to this invention the pentabasicsalt may be. produced in substantially pure? condition by ceasing to addsalicylic acid when the pH drops topI-I:8.3; mixtures of pentabasic andmonobasic lead salicylatesmay be produced by ceasing to add salicylicacid before the pH begins to drop below pH :8.3. and. the monobasic saltmay be produced" in. substantially purev condition by ceasing to add.salicylic acid when the pH value begins to drop below pH:8.3.. Inpractice the drop: in pH is so rapid and. abrupt that. upon completionof the.

formation of the monobasic salt the pH value of the suspension. isfound. to be. at pH:4.8- at which point if ad ditional salicylic acid.is added,

the. normal leadsalicylate would be formed.

Since the monob'asic salt represents the combination of two mols of Pwith two mole of. salicylic acid and the. pentabasicsal t represents thecombination of sixmols of 9130 with two mols of salicylic acid; thesesalts may be prepared according to the invention by bringing together inthe manner described, amounts of the respective components in these molrelations. Eirpressed in terms of percentage, the amount of.

salicylic acidm'ay varybetween about 20;6% (for the pentabasic salt) andabout 62.0% (for the monobasic salt) based upon the weight of PhD 3 inthe lead monoxide suspension. Preparation of these salts will beillustrated by the following examples.

EXAMPLE I Pentabasic lead salicylate A slurr comprising 1340 grams (6mols) of lead monoxide, '7 liters of water and 3 grams of lead acetatecrystals was moderately agitated in a suitable vessel at roomtemperature. To this suspension was added at a slow, uniform rate over aperiod of about 2 hours, 276 grams (2 mols) of finely powdered salicylicacid, an amount calculated to be just suificient to combine with thelead oxide to form the pentabasic lead salicylate. As the reactionprogressed, the color of the slurry gradually changed from brownishyellow to lighter shades, until when all the salicylic acid had beenadded, it was a, snow-white color. This end point was furthercharacterized by an abrupt change in the pH value from a previouslyconstant value of about 9.9 to about 8.3, at which time all the leadoxide had been converted to pentabasic lead salicylate. This reactionwas completed at room temperature. The white product composed ofaoicular crystals, after filtering and drying, contained 83.8% leadoxide and 16.2% salicylic anhydride and its specific gravity was 5.11,and it had a mean refractive index of 2.05, and an ex-- tinction angleof between 282 and 31.7".

EXAMPLE II Monobasic lead salicylate A slurry comprising 446 grams (2mols) of lead monoxide, 2.5 liters of water and one gram of lead acetatecrystals was moderately agitated at room temperature in a suitablecontainer. There was then added slowly and uniformly over a hour period,2'76 grams (2 mols) of finely powdered salicylic acid. During theprogress of the reaction, when 92 grams of acid had been added it wasnoted that the slurry turned white and this indicated the formation ofthe pentabasic lead salicylate, with an attendant decrease in pH valueof the liquid phase from about 9.9 to about 8.3. The acid addition wascontinued until the entire calculated amount was added, whereby thepentabasic lead salicylate was converted to the monobasic leadsalicylate as indicated by the fact that the pH value which had remainedfairly constant at about 8.3, finally dropped at the end to about 4.8.The white product, after filtering and drying, contained 63.4% leadoxide and 36.6% salicylic anhydride and its specific gravity was foundto be 3.82. It had a mean refractive index of 1.90, and an extinctionangle of between 162 and 250.

The reactions illustrated in the above examples may, if desired, beoperated at elevated temperatures up to the boiling point of water andthey may be conducted without the aid of the lead acetate used or anyother catalyst.

During the course of the preparation of the products of this inventionby the successive addition of salicylic acid to a slurry of lead oxide;

the most basic compound is formed first and when the PhD content isabout 83.8%, the product is pentabasic lead salicylate; when it is about63.4%, the product is monobasic lead salicylate, the product of thesecond stage. While it has been shown that it is thus possible to formtwo different basic lead salicylates, both novel, namely, the penta- Thelead salicylates of the present invention are" useful as pigments andmay be employd either alone or in combination with other pigments informulating improved coating compositions.

I claim:

1. A process for preparing a basic lead salicylate selected from thegroup consisting of pentabasic lead salicylate, monobasic leadsalicylate, and mixtures thereof, which comprises forming an aqueousslurry of lead monoxide, PbO, and while agitating the same, graduallyadding thereto salicylic acid in an amount between about 20.6% and about62.0% based upon the weight of PhD in said slurry.

2. A process for preparing pentabasic lead salicylate which comprisesforming an aqueous slurry of lead monoxide, P100, and while agitatingthe same gradually adding thereto salicylic acid in amount about 20.6%based upon the weight of PhD in said slurry.

3. A process for preparing monobasic lead salicylate which comprisesforming an aqueous slurry of lead monoxide (PbO) and while agitating thesame gradually adding thereto salicylic acid in amount about 62.0% basedupon the weight of P in said slurry.

4. A process for preparing a basic lead salicylate composition whichcomprises forming an aqueous slurry of lead monoxide, PbO, containing asmall amount of a salt selected from the group consisting of thewater-soluble nitrates and acetates of lead, and while agitating thesame gradually adding thereto salicylic acid in an amount between about20.6% and about 62.0% based upon the weight of the PbO in said slurry.

5. A process for preparing pentabasic lead salicylate which comprisesforming an aqueous slurry of lead monoxide, PhD, and while agitating thesame gradually adding thereto salicylic acid until the pH of said slurrybegins to drop below 9.8 and then discontinuing the addition ofsalicylic acid.

6. A process for preparing monobasic lead salicylate which comprisesforming an aqueous slurry of lead monoxide, PbO, and while agitating thesame gradually adding thereto salicylic acid until the pH of said slurrybegins to drop below 8.3 and then discontinuing the addition ofsalicylic acid.

'7. As a new composition of matter, a basic lead salicylate compositionselected from the group consisting of pentabasic lead salicylatecorresponding to the formula 5PbO.Pb (CeI-IrOI-LCOO) 2 monobasic leadsalicylate, corresponding to the formula PbO.Pb(CsH4OH.COO)2, andmixtures of the same.

8. As a new composition of matter, pentabasic lead salicylatecorresponding to the formula 5PbO.Pb (Cal-14011000) 2.

9. As a new composition of matter, monobasic lead salicylatecorresponding to the formula, PbO.Pb(CeH4OI-I.COO)2.

10. As a new composition of matter, a mixture of pentabasic leadsalicylate corresponding to the formula 5PbO.Pb(CsI-I4OH.COO):2, andmonobasic lead salicylate corresponding to the formulPbO.Pb(CsI-I4OH.COO)2.

LEONARD M. KEBRICH.

